1. Field of the Invention
The present invention relates to a display control device for controlling a display gradation in each display dot of a liquid crystal display device and the like, based on an image data (gradation data) written into an image memory such as a VRAM and the like, and to a display apparatus having the display control device.
2. Description of the Related Art
FIG. 6 is a block diagram showing a structural example of a conventional display apparatus.
In the figure, a screen size of an liquid crystal display panel (hereinafter, it refers to "LCD panel") 1 is a width 320.times.a length 240 pixels, and each pixel is constituted of 3 dots such as R (Red), G (Green), and B (Blue).
Also, a storage capacity of an image data storage unit 3a which is constituted of an IC memory such as a VRAM and the like, is 320.times.240.times.3.times.4=921,600 bits=115,200 bytes, and as corresponding to each display dot (320.times.240.times.3 dots) of the LCD panel 1, the gradation data of 4 bits is allocated thereto, respectively. As a result, in each display dot of the LCD panel 1, 16 gradations, i.e., the gradation displays of (0000) 2.about.(1111) 2 are made possible. Further, in FIG. 6, two image data storage unit 3a are provided for use in a front screen and for use in a back screen since they might perform an image switching process.
A driver 102 drives the corresponding display dots one after another on the LCD panel 1 so as to turn them to be the gradation displays shown by the gradation data, when the gradation data (DA) is inputted from a controller 105 in synchronization with a predetermined clock.
In the configuration as described above, a CPU 4 writes an optional image data (the gradation data for 1 screen) into the image data storage unit 3a.
On the other hand, the controller 105 reads, whenever a predetermined frame signal (a pulse signal with an interval of 1/150 seconds) is inputted, the gradation data in the image data storage unit 3a from a head address one after another, and then transfers each of the gradation data being read, together with an address thereof, to the driver 102.
The driver 102 drives the display dots corresponding to the transferred addresses so that they would turn to the gradation display indicated by the gradation data transferred therewith.
As the above described processes are repeated whenever the above-mentioned frame signal is inputted, the image corresponding to the image data written into the CPU 4 is displayed on the LCD panel 1.
Meanwhile, in the conventional display apparatus described above, since the controller 105 reads all of the gradation data in the image data storage unit 3a whenever the frame signal is inputted, and then transfers all of the gradation data being read to the driver 102, in a case that the image size of the LCD panel 1 is large (for example, in a case of the width 320.times.the length 240 pixels and the like, as shown in FIG. 6), the quantity of data transfer between the image data storage unit 3a and the controller 105, and the one between the controller 105 and the driver 102 turn to be very large.
Accordingly, there was a problem that the dissipation currents used for the data transfers are very large in the conventional apparatus.
For such problem, the applicant of the present invention had filed the Japanese Patent Application No. 9-5874 disclosing the display control device and the display apparatus which reduce the quantity of data transfer between the respective units (the driver, the image data storage unit, and the controller) of the display apparatus, and suppress the dissipation currents to much lower, by providing, inside the driver, a built-in memory which holds a current display content of the LCD panel, as well as by providing a memory which holds a storage location (in the image data storage unit) of the data showing an intermediate gradation (the gradation degree that is larger than 0%, but less than 100%).
Furthermore, in the LCD panel, there is a case that a cursor is also displayed besides the image corresponding to the above mentioned image data.
In this case, in the conventional display apparatus, whenever the frame signal is inputted (i.e., for each frame), the data about the cursor display is transferred to the driver.
For this situation, in the above-mentioned apparatus by the applicant, it is not ensured that all of the gradation data is transferred whenever the frame signal is inputted because of the above mentioned feature (i.e., reducing the quantity of data transfer between the respective units of the display apparatus).
As a result, in the above-mentioned apparatus by the applicant, there is a problem that a cursor can not be displayed clearly without glimmering, by the same processes as the conventional apparatus.